1. Field of the Invention
The present invention relates to a dielectric thin film, a thin film dielectric device, and a method of production of the same, more particularly relates to a dielectric thin film, thin film dielectric device, and method of production of the same giving a high dielectric constant and able to reduce the leakage current.
2. Description of the Related Art
In recent years, in the field of electronic devices, along with the higher densities and integrations of electronic circuits, increasingly smaller size, thinner layers, and greater capacitance are being demanded from the circuit devices required for various electronic circuits such as capacitors.
To reduce the size and thickness of layers and increase the capacitance of capacitors, dielectric materials with high dielectric constants are being used. As these dielectric materials, lead titanate (PbTiO3), lead zirconium titanate (PZT), barium titanate (BaTiO3: BT), stronium titanate (SrTiO3: ST), barium strontium titanate (BaSrTiO3: BST), and other perovskite-type oxides may be mentioned.
Among these, barium titanate (BT), strontium titanate (ST), and barium strontium titanate (BST) have high dielectric constants and long life time and are superior in properties. In particular, the full solid solution of barium titanate (BT) and strontium titanate (ST), barium strontium titanate (BST), can be adjusted in Curie temperature by changing the ratio between BT and ST and can be made a paraelectric substance having a high dielectric constant even at room temperature.
Further, such a capacitor, for example, a capacitor device used as a circuit device essential for various electronic circuits, sometimes has to be made a thin film device. Therefore, the BT, ST, and BST used as the dielectric layers of the capacitor device also have to be made thinner to be made dielectric thin films. When making the above dielectric materials the dielectric thin film, it is desirable that the dielectric constant be high and the leakage current be reduced.
However, in such a dielectric thin film, achievement of both a high dielectric constant and low leakage current is generally considered difficult. To solve this problem, the method of doping an additive in the BST has been performed. For example, Japanese Unexamined Patent Publication (Kokai) No. 8-198669 proposes an Er-doped BST comprised of BST doped with erbium (Er). However, when making the BT, ST, BST, or other dielectric a thin one of less than about 500 nm, it is difficult to uniformly add the additive Er and the distribution of the additive becomes varied, so it is difficult to obtain stable characteristics.
Further, Japanese Unexamined Patent Publication (Kokai) No. 7-17713 discloses a dielectric thin film comprised of a perovskite type oxide expressed by the chemical formula (Ba,Sr)yTiO3 where 1.00<y≦1.20. A higher dielectric constant and a lower leakage current are achieved. In the examples of this document, the composition of BST forming the dielectric thin film is made (Ba0.5, Sr0.5)yTiO3 where the ratios of barium and strontium are equal and the value of “y” is made 1.00<y≦1.20. However, when making the composition of BST the above range of composition, both a high dielectric constant and low leakage current cannot be said to be sufficiently achieved yet. In particular, when making a dielectric thin film even thinner (for example, when making it less than 100 nm), both the dielectric constant and the low leakage current characteristic cannot be said to be sufficient.